One class of processes for removing materials from microfeature workpieces uses abrasive particles to abrade the workpieces either with or without a liquid solution. For example, mechanical and chemical-mechanical processes (collectively “CMP”) remove material from the surface of microfeature workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a head 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F) and/or reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The head 30 has a lower surface 32 to which a microfeature workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 in the head 30. The head 30 may be a weighted, free-floating wafer carrier, or the head 30 may be attached to an actuator assembly 36 (shown schematically) to impart rotational motion to the workpiece 12 (indicated by arrow J) and/or reciprocate the workpiece 12 back and forth (indicated by arrow I).
The planarizing pad 40 and a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the workpiece 12. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the microfeature workpiece 12, or the planarizing solution 44 may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and clean non-abrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the microfeature workpiece 12 with the CMP machine 10, the head 30 presses the workpiece 12 face-down against the planarizing pad 40. More specifically, the head 30 generally presses the microfeature workpiece 12 against the planarizing solution 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the head 30 moves to rub the workpiece 12 against the planarizing surface 42.
Conventional CMP processes that use abrasive slurries may not produce adequate results because it is difficult to consistently produce a uniformly planar surface across the workpiece. The planarity across the workpiece is a function of several parameters; one such parameter is the distribution of abrasive particles between the workpiece 12 and the planarizing surface 42. The distribution of abrasive particles, however, is difficult to control because the leading edge of the workpiece 12 wipes the planarizing solution 44 from the planarizing surface 42. As a result, there is generally less planarizing solution 44 and thus fewer abrasive particles at center of the workpiece 12 compared to the edge of the workpiece 12. The center region of the workpiece may accordingly have a different removal rate than the edge region.
A useful technique to improve control of the distribution of abrasive particles is to use fixed-abrasive polishing pads. Fixed-abrasive pads have a matrix and abrasive particles attached to the matrix. For example, several existing fixed-abrasive pads have a resin binder and small abrasive particles suspended in the binder in a desired distribution. The abrasive particles at the surface of the fixed-abrasive pad are held in place by the matrix such that the center and the edge of the workpiece consistently experience a well-controlled distribution of abrasive particles.
Fixed-abrasive pads, however, may have several drawbacks. One drawback of using a fixed-abrasive pad is that the workpiece can skip, chatter, and/or stick relative to the surface of the fixed-abrasive pad. This can produce scratches or other defects in the workpiece. Therefore, even though fixed-abrasive pads are promising, additional development is needed to use them for the production of many types of microfeature devices.